The extension of the studies of partial replication of UV inactivated bacteriophage DNA will be the main goal. The objective is to localize the areas within the UV inactivated T4 phage genome, which after single infection, are able to replicate repeatedly, generating a pool of fragments containing genetic information clustered around the origins of replication. Both physico-chemical and genetic experiments will be performed. In the physico-chemical approach, the extent of replication in double labeling experiments - the amount of new DNA produced, and its size (depending on the dose of irradiation) will be determined. In genetic experiments, the genetic make-up of partial replicas will be analyzed. This will be done by infecting bacteria with a UV inactivated mutant of T4 phage (imm/sp) which does not exclude superinfecting bacteriophages. At intervals after infection, superinfection with rescuing viable phage, of a different genetic makeup will follow. Rescue and amplification of certain genes will be analyzed as a function of the dose and timing of superinfection. Preliminary experiments, performed in cooperation with Doermann assure us that amplification of UVed phage genomes does indeed occur for certain genes. Saturation experiments using multiple ambers will be performed, and the genetic makeup of the resulting progeny will be analyzed in both lysates and single burst experiments. The results should allow identification of the locations of multiple initiation sites in T4 phage DNA. The genetic part of this experiment is presently being performed in cooperation with A.H. Doermann. BIBLIOGRAPHIC REFERENCE: A.W. Kozinski and A.H. Doermann (1975) Repetitive DNA Replication of the Incomplete Genomes of T4. Proc. Nat. Acad. Sci., USA 72: 1734-1738.